Yup. Even seeing that Oberyn would even go near Mace Tyrell shows that something was up.

Btw, Oberyn's the best character in the series by a large margin.

Oberyn is badass, but I think my favorite character is Jamie Lannister - I love the complexity of him and how on the surface he looks like one thing, but underneath all the armor and bravado he's such a complex, but yet simple creature.